Low frequency transformer



April 2, 1935.

Y J. POLIAKOFF- LOW FREQUENCY TRANSFORMER Filed June 15, 1932 wax M ATTORNEY 2 Sheets-Sheet 1 Joseph Poliakof! April 2, 1935. J. POLIAKOFF LOW FREQUENCY TRANSFORMER 2 Sheets-Sheet 2 Filed June 13, 1932 INVENTOR Joseph Poliukofr W ATT ORNEY Patented'Apr 2,1935; 9 Q

I The present invention ,re1ates ;to improvements in audio frequency transformersand transforrher circuits, such-as intervalveii transformers andccu-{ pling transformers between gramophone;g pic};- upsymicrophones and the :like and grid circuits v offvalves; usedin wired and wirelesstelephony,

'SllOfiflifiGIt-EDCGS in the characteristic curve s'are obtaineil' either by having an unequal numberoff *tu'rn's in such parts of thesecondary circuitand/or by the employment of r'esi's'tiige and/ or capacitative v as well as in various sound reproducing apparatus such as talking filni-apparatus, public "address systems; electrically" reproducing gramophones forramplifiersin a'ids for deafness apparatus and.

forlikeipurposes." i 1 This invention consists in the construc 1o of audio. frequency transformers such a; ;way:that

the frequency-amplification curve oi-rthe t-rans former can be given themost advantageouszshape for. the particular workingconditions; oonsiclerm'g the whole apparatus'inwhich the transformeris includfi. 3 w n It hasrhitherto b'en' rproposedutcplace esiste ancesflndu'ctances con'dens'ers intl'l'e rmry, secondary :or tertiary circuits :.of 'individual' elejce tri'c transformers, :forpurposes 'o'f increasingssta bility of working; obtaining? greater uniformity "of amplification, suppression 'or prcductionrefresonancesand foriqtherpufposes'."

21.My inventich provides for acomplete andJcom unuous controrof the shape'of the response curve oftransifo-rmer and transformer circuitsfallowing it Etc: have practicallyv any shape and" I tilt up 'or 'clowifi-it beihgf'sufi'cient to" emp1oyo'nly the Secondary 'and. primary'windings of the transforiiir. i'According to this inventidn," wherein. sec on'dary 'circuitydivided into two or more parts 'c'cnn'cted in "series "and mounted on t e: same *ih i' fii lbfi core: is: 1 employed; the control "of the {response curve of the transformer-is 'eif'ecte'dby construct ing such parts; 'which'may act either to'assi'st one another 'or clifferentiallyi in 'such -a' manner as 'to givethem frequency amplification curves of diffeiv'ent; characteristics; Tmeans being pro ided to a control the frequency amplification curves tobe varied to suit 'changing conditions "of working the apparatus and. varying 'requirenients The einventio "provides methods of summing the effects of the'various parts such a. Way that the r l ant6u YQ an J v n a y s ape from .a: sharply fa1li11'g":curve?thr0ugh; a :substantially straight line t'o a curjve having a steeply'rising characteristim'as well as loopedicurves. v

- Referring'to the drayvin liorin er circuitac'cording toln y invention;

h op a i n of he ir ui pfiFi sl f le h gvablememher :Q mnetnt vid r 's.- .andgsi have differentf gharacteristics; that is;

. fA "transformer II V Q T i re 7 1 ,i ow athep mar and nda y w n ing f a, ansf rme w t e v cqnd r zdi vr fl 11 th t ynw ,8 ,5 t-Wh c t t itls' is shown shunted yaicondensen 0 in Serie With e jev i te ei p r 0 is ma kedi i h cisthe i pen ar m ne sli rcqnne ted .theg'esistance r-;' of vw hich 5 QQnnected-in parallel 1 Aemdsg; m-gihieqeeeitne e1- uiegwin V e gein mheriq urwsso vva iq s ha es "by sm i hessin ten sin uma thateoils transiqriner'sffplfm f, n a d iii lqr e nqzwnd 0i aw u mave difiegent frequen m fic tion-curyes Y i a 1 V ew t -jeiollowi e t ts giving su ve showing maxima bothfi the lotif and highjre quen l enq ottheiu s acou sm e 0M zc v z' h me uiteb eifd he om ensation h attenuetion of theie'nds; of theiscale reproduce, r adc st n cq de m i n e h,

s; I IWereJyyouncl-on separatefbobe' n bins placed on l the" central limb of Q-a' three I limb laminatiqns of nickelrironalloy -g "T.

The s coil is made to resonate with -the-';jshunt capacity 1c: and; its} distributedacapacity 'a.t;the I V v 7 50. Y "p oeress v y1 e1lin rr wwhi e t isflipqilwhas:"i, r a substantiallyrstraightcurve except' forra'sharp' M sne na e-zin th ?h ehir u nq 40 p rtp w .low frequencyf,end'bf the acousticscale and hasfla W en h We @9 erew ne te seri sn ur eith; o mexima- 'iv z md p d-linste d wozs milarco s;0;l14 5 .-t t e@are c n dfiii series, the high" f r'equency;end of; the scale will be attenuated, for, the high frequency resonance:

.will oc ur at 81120 1 z oflQ andthere will b has for V V closedlinaighetic circuitrcorei consisting; cfithinv ii.

- 'I'hus means are provided'for changing, a;

r V- N h r the, w r u c th seele e be effectively controlled so 7 as' to permit change from a looped toa rising curve by means of the potential divider connected facrossthe s1coi1:'as

shown in Figure l. The motion of the moving 1 istreversed, the'coil s'f begins to resonate with the icondenser 'c' The frequency of the resonance member it mixes the contributions of.c1oils;s"

and s in different proportions; wh g' gfitmqyn ing member a is at. the extreni e right a sharply rising'curve is obtainedysince the is, {coil con- Q tributes nothing to the resultant,jcurve ,-f but greatly. reduces the lowfrequency compo'n'ent' c'ontributed by the s" coil,"leaving the highLfrequenW 15 i unaffected.

Asj-the movablemeniber travels" to: the'left the low frequency end ofthe; curve is progressively 1 'raisedfright up toth'maximuni curve to arising curve or any' ciirve interme iate between'a' looped and rising curve. 7

' The circuit in-Figure' -Z shows thesecondar'y.

I made in two partss,-s"'acros1the ends of which.

there are connected two'condensersc', =c'-' having the resistance-Wei a potential divider connect ed between themgthe movable member a of which is connected to thejunction be'tweerf the-Ftwo parts of'the secondary} Eachbf such parts'can, be made to resonatewiththe ceiidenserscand 'e" in turn by sliding the ontact attachedto their junction t'owar'ds an; c :The resistance 1% joining 'the-jtwo conden'Sers can 'be f inade'i high enough to damp out the resonance ef=-theiwhole j of the secondary with the two-condensers"in series or it may bemade-low enough to preserve it at any desired magnitudei 7 "I This circuit enables amplification of either end. of the acoustic 'scale 'or fany'other part thereof to r be raised above that of the :rest'of I the; scale,

but does not enable ither end to be depressed below the, average amplification level. i

Figure 3. shows 'acircuit which is identical withthat of Figure 2 exceptithat one of the con,- rden s, f, is d nsed with-; B is. rmee sve circuit is obtained capable 'of'boosting ,up.either endor any oth rtntithe-eurxn;andidepieseine V the part correspondinglto .;lo and middle fre-- circuit. is connected to the;+,I-I. T., e. the-posiquenciestoyany desired low levei.

' ores owerdstne condenser c greater and Lgsharper resona.nce, is produced *(in the lowrfrequencyend or any other point of the'curve) while motion-tothe; right 7 will reduce the resistance across 'the -funtuned Y creasing resistance." r I I When theconnections of the movable rnember a the potential divider"and of the end of the 3 resistance r "connected? to 'the end of the .part

of resistance across a 1 portion thereof tends (to raise the amplification givento the'high frequencies, which effect generally :-inerea's ed with de sf of thefs ecdfida'r y '(Figuifefilgare interchanged;

assho'wn 'in- Figure45a complete cont rol of the curve is obtainedvas shownjon thef curva- Figure 4a.; "Ihe' fmotion" of the rhovable ember a( changes the sharply-falling curve 1 having a boost at the low frequenciesfthrough{afcomparatively straight line 1 curve i If to a. sharply rising curve -w thama immn at'3ooo-";-

. y f the connections of ther m-bvablewmember a" in; the lowfrequency part and a falling curve ad ju'stable' to a; substantially straightccurve withj-out peaks in -the high frequency part. 1

and the outer end of the condenser c" (Figure 2) are reversed the-circuit obtained is as shown in Figure l jincluding the dotted condenser 'c a As the movable member a travels to the left the wholeof the secondary resonates with c 'givingalow frequencyboostand a falling curve. =Whenthe-direction 'of motion 'of the member (1' can beconvenientlyfixed in the high frequencies, so that any curve intermediate between a sharply In, both circuits of Figure 4 additional curve {adjustment {may be provided V by winding the nts in the opposite-sense toi the part s; '-"-f' Thisf-reversalis usefuhmainly for the purpose ofproviding a -ourve gwithjan adjustable boost i The-JOWLf-requency boost 'is produced by resonan'ce .ofltheiwhole secondary with condenser while thehigh frequencypeakdue to theadis- 'tributedlcapacity' of s is taken ofhby making s? and} t -resonate atthe frequency of the peak, which" de presses the peak owing to the differential action of sand s. r I

Figure =showsf anotherxform of the transformerwherein the sectional coils" is wound differentially as shown or it maybe wound in the same sense,-wit h respect to the coil s. The low frequencyboostf and the falling curveare here produced by means of; a condenser c'.".,' one. end

offwhichisconnected to one end of the primary winding 4), its other end; being connectedzto one end of the potentialxdivider r, the movable memher; a .ofwhiclr is connectedzto thev outer-end of the coil 's" and the oth er endtothe junctionof thecoils sands'fl. VIn thisycircuit the free end of} the :coil sf is, connected to the grid of the ,valve', ithefreeend ofthe other secondary-coil 3" being connected-toythe grid bias G. 13. whilst the end ofrthe primary coil pitot which the condenser ccfl'; is1connected',--is itself connected to. the plate I! of the ivalve. Theother end of the-primary tive ,."of5thee-battery or other source of electric 'pressurelror to-the grid bias, G. .B.,v if the transformer is iresistanceffediw i The operation of ,this circuit obviously depends on; the existence of a: low impedance path between thevG. 3.. end of the secondary and the i-t-H; T. end of the primary; Consequently this Y circuit, can only. be used: for. intervalve coupling,

its; usew jforn other purposesqbeing possible only if is operated as an auto-transformer.

Figure 5a shows three overall amplification curves of a '2-valve" audio frequencyamplifier,

thejtwogvalves'bemg coupledsbyl a, transformer constructed as shown ingFigurefi a I The constants of the transformer were: W gi nmar mrns=4oooi bunq wn 44.s.fw. G.

1 s =21000wouhdwith46 sown. Secondary turns s"'=3500 wound with 46 S. W. G. v; I a 5; c: =.025 micro-farads.

'I 'he figure showsthat a very "oomplete control of the overall curve isiprovided by this'circuit. Vlfl ren themovable membera is in its lowest position, the falling curve I is'obtained, an intermediate position of the member 0 yields the substantially straight linecurvelI andthe upperfrequencies. Y t

The three curves in Figure 6a have been taken most position of the member it yields the rising curve III. I

For many purposes, such as correctingthe at-' .tenuation in the high frequencies of the acoustic level without appreciably affecting the high frequencies.

The circuit illustrated in Figure 6 gives the desired variation in response curves- The secondary consists of two equal or unequal coils s and s", s' being shunted by a high resistance T, 'which forms the resistance of the potential divider, one end of s" going to the G or G. -B.-of

the next valve, and the other end to the movable member a of the potential divider. T j

The motion of the slider has vbeenffound to control the amplification of low'and middle frequencies without afiecting appreciably the high of a transformer according to Figure 6' with the following constants: I V

Primary 0011:4000 turns woundwith 44 S. W.

G. wire.

Coil s'=17,000 turns wound with 47 S. W. (3,;

wire. r i

Coil s"=17,000 turns woundwith 47 S. W. G.

' v phones, photoce1ls,-and the like to' grid circuits of valveswith 'asecondary divided intotwo partsa'rrangedfon the same core and connected soas toact in opposition to one another, one of said parts of the secondarybeinggshunted by theresistance of a'potential dividen-ythe 'movable U I member of which is .connected'tdone end-of the wire. Potential divider 0.5 megohm.

Curve I is obtained when the movable contact" a a is in itsextreme left handposition, Curve II in an intermediate position, and Curve III when in its extreme right-hand position.

. Ithas been found advantageous to form some ofthe capacities used the several circuits above described by bifllar winding on the'cores of the transformers, which when inductiveprovide additional means ofcurve control. The

wire could if desired, be replaced by suitably insulated metal strips; f

potential dividers, or the variation can beeffected by 'means of tapplngs and a suitable switch.

. In all figures, .eircept Figures, the secondaries, and primariescanbe connected either way roundwith respect to the valves or circuits they couple.

In all the above circuits the continuously variable potential dividers may be replaced by fixed Herein'above I have spoken of division of the I secondary. into two or more parts, the-'worddivisionis to be understood in the electrical sense and not necessarily in the mechanical sense, since it may bev effected eig. by; providing a tapping-v in a single coil. I

I claim:

' I An audio frequ'encv'transformerv for inter?v valve coupling, or forcoupling pick-ups, microphones, photocellsfand thef like to grid circuits 1 of valvesjwith a secondary divided into two parts connected in series, a shuntto one of saidparts of the secondary, said 'jshunt' comprising a con-i denser and the. resistance or a potential divider connected in series, "the movable member of the potential divider being connected to the oute! 1 terminal o f'the other part of the sectmdary 2. .An audio" irequency transformer for intervalve coupling, or for coupling pick-ups, micro 

